1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
There is a conventionally-known technology for automatically supplying toner from a toner container to a developing unit in an electrophotographic image forming apparatus. In order to make the developing unit stable during toner supply, there is a need to perform control on supply, i.e., the amount of residual toner in the developing unit is detected with as high accuracy as possible, and supplementary toner is supplied gradually, whereby the ratio of the residual toner to the supplementary toner is maintained constant just after the toner is supplied. For example, Japanese Patent Application Laid-open No. 2007-233091 discloses a technology for detecting the amount of residual toner, i.e., a technology of using an optical detection unit installed in a developing unit.
However, in conventional image forming apparatuses that use an optical toner detection unit, it is determined that “toner is not present” when light is transmitted, and it is determined that “toner is present” when light is not transmitted; therefore, if a light emitting/receiving element has an operation failure, connection failure, or optical path misalignment, it is determined that there is a sufficient amount of toner in the developing unit. As a result, it is difficult to determine whether there is actually a full amount of toner or a full amount of toner is falsely detected due to a failure of the detection unit. If a full amount of toner is falsely detected, the amount of toner in the developing unit is undetermined.
If there is no toner in the developing unit, and if printing is continuously performed, developing rollers and photosensitive elements may be damaged; therefore, if the amount of toner in the developing unit is not properly determined, the apparatus needs to be forcibly stopped regardless of whether the full amount of toner is detected or the full amount of toner is falsely detected. Hence, a method is implemented to prevent the apparatus from being forcibly stopped when the full amount of toner is normally detected, that is, the supply amount is controlled so as to prevent the toner from filling the developing unit; however, the amount of toner to be supplied from the toner container per unit time varies widely, and it is difficult to control the amount of toner in the developing unit so as to always prevent a full amount of toner. Thus, there is a problem in that the apparatus is forcibly stopped each time there is a full amount of toner in the developing unit.
In consideration of the foregoing, there is need to provide an image forming apparatus that is capable of preventing false detection as to whether there is a full amount of toner in the developing unit.